This invention relates to the field of polymer films and methods for forming such films, and in particular, to a film possessing a polyolefin core layer faced on each side thereof with a transition layer containing a polydialkylsiloxane additive, and a polyolefin skin layer on the outside of each tie layer.
Heat sealable multilayer films which are useful as packaging materials are known in the art.
U.S. Pat. No. 4,343,852 describes a uniaxially or biaxially stretched composite film packaging material of from 5 to 200 microns total thickness possessing a propylene polymer base film and at least one surface film containing at least two of (a) an ethylene-propylene (EP) copolymer, (b) a propylene-alpha-olefin copolymer and (c) a copolymer of butene and any other alpha-olefin. The propylene polymer base film can contain any one of a variety of additives, e.g., a lubricating agent such as a fatty acid amide, and each surface film can contain from 0.01 to 0.15 parts by weight of a silicone oil to improve its coefficient of friction in the heated state and reduce its slide resistance caused during hot plate seal by an automatic packaging machine. Examples of silicone oils which are said to be useful for this purpose are polydimethylsiloxane, polymethylphenylsiloxane, olefin-modified silicone, polyether (e.g. polyethylene glycol, polypropylene glycol)-modified silicone, olefin/polyether-modified silicone, epoxy-modified silicone, etc. U.S. Pat. No. 4,343,852 is incorporated herein by reference in its entirety.
U.S. Pat. No. 4,400,428 describes a heat sealable, multilayer film packaging material possessing a biaxially stretched polypropylene film as the base film, an adhesion-promoting layer of modified polyolefin, a gas-barrier layer of hydrolyzed ethylene-vinyl acetate copolymer and a heat-sealing layer of olefin polymers, wherein the base film carries on at least one surface an optionally at least monoaxially oriented layer combination consisting of: (a) a heat sealable outer layer of polyethylene or of an ethylene copolymer containing at least 3%, and preferably at least 4%, by weight of ethylene; (b) an adhesion-promoting layer of modified polyolefin; (c) a gas-barrier layer of a hydrolyzed ethylene/vinyl acetate copolymer containing from 50 to 80 mole percent of vinyl acetate units of which at least 90% by hydrolyzed; (d) an adhesion-promoting layer of modified polyolefin; and, (e) a layer of polyethylene or of an ethylene copolymer containing at least 3, preferably at least 4% by weight of ethylene. Layer (a) contains an additive combination consisting of: (1) from 0.3 to 1% by weight, based on the sealable layer, of a long-chain aliphatic amine; (2) from 0.1 to 0.7% by weight, based on the sealable layer, of a dispersed thermoplastic polymer which is incompatible with the polyethylene or ethylene copolymer and which has a softening point at most 50xc2x0 C. below or above the softening point of the polyethylene or ethylene copolymer; and, (3) from 0.1 to 1.2% by weight, preferably 0.2-0.7, based on the sealable layer, of a polydialkylsiloxane, preferably polydimethylsiloxane. The foregoing additive combination is said to produce a multilayer film having very good slipping properties combined with good machine processibility compared to known multilayer films containing known type lubricants such as the fatty acid amides, e.g., erucamide. U.S. Pat. No. 4,400,428 is incorporated herein by reference in its entirety.
U.S. Pat. No. 4,419,411 describes an oriented multilayer polypropylene film structure comprising coextended layers of: (a) a base layer comprising polypropylene of comparatively high stereoregularity, the precursor resin of which contains an amide of a water-insoluble monocarboxylic acid having about 8 to about 24 carbon atoms, e.g., erucamide; (b) a skin layer comprising a polyolefin of comparatively low stereoregularity on at least one surface of (a), said skin layer containing a surface-modifying proportion of a combination of finely divided silica and a silicone oil such as a 30,000 centistokes polydimethylsiloxane; the surface of skin layer (b) having bloomed thereon a surface-modifying proportion of at least some of the amide of base layer (a). U.S. Pat. No. 4,419,411 is incorporated herein by reference in its entirety.
U.S. Pat. No. 4,502,263 describes a heat sealable polyolefinic multilayer film possessing a base layer comprised of a propylene polymer and at least one sealable layer containing at least one propylene copolymer, at least one low-molecular weight resin and at least one polydiorganosiloxane, wherein the sealing layer comprises a combination of: (a) from about 68.5 to 89.7% by weight, based on the weight of the sealable layer, of an olefin resin composition comprising an ethylene-propylene-butylene terpolymer and a propylene-butylene copolymer, corresponding to a content of from about 0.1 to 7% by weight of ethylene, 53 to 89.9% by weight of propylene and 10 to 40% by weight of butylene, based on the weight of the olefin resin composition; (b) from about 5 to 15% by weight, based on the weight of the sealable layer, of a low-molecular weight resin, which is compatible with the olefin resin composition; (c) from about 5 to 15% by weight, based on the weight of the sealable layer, of a propylene homopolymer; and (d) from about 0.3 to 1.5% by weight, based on the weight of the sealable layer, of a polydiorganosiloxane such as any of those referred to above. U.S. Pat. No. 4,502,263 is incorporated herein by reference in its entirety.
U.S. Pat. No. 4,692,379 describes an oriented, heat sealable polymer film laminate possessing a low coefficient of friction, good receptivity for water-based coatings and good optical clarity and a method for manufacturing. U.S. Pat. No. 4,692,379 is incorporated herein by reference in its entirety.
U.S. Pat. No. 4,734,317 describes a polyolefin film having a base layer composed essentially of propylene polymers and having sealing layers present on both sides, composed essentially of sealable olefin polymers. Polydialkylsiloxane is incorporated in a first of the two sealing layers, and this layer is not subjected to corona treatment. The second sealing layer is subjected to corona treatment and has polydialkylsiloxane, not incorporated, but present on its outer surface, the polydialkylsiloxane having been transferred to this layer by contact with the sealing layer in which polydialkylsiloxane is incorporated. The relative polydialkylsiloxane occupancy on the second layer, which is determined by means of ESCA spectroscopy, is not more than 15. The three-layer polyolefin film is prepared by a coextrusion process. It is particularly suitable for use as a packaging film on high-speed packaging machines. U.S. Pat. No. 4,734,317 is incorporated herein by reference in its entirety.
U.S. Pat. No. 6,087,015 describes a thermoplastic film having a matte surface comprising: a core layer of a thermoplastic polymer, the core layer having a first side and a second side, and a matte surface layer on a first side of the core layer, the matte surface layer comprising a blend of (i) a copolymer of ethylene and propylene or a terpolymer of ethylene, propylene and a C4 to C10 alpha-olefin or a propylene homopolymer; (ii) an ethylene polymer and (iii) a polydialkylsiloxane selected from the group consisting of (1) a polydialkylsiloxane having a number average molecular weight above about 250,000, typically above about 300,000 and a viscosity of above about 10,000,000 cSt, usually ranging from about 15,000,000 to about 20,000,000 cSt., and (2) a polydialkylsiloxane functionalized polyolefin. The external surface of the matte surface layer demonstrates a coefficient of friction ranging from about 0.1 to about 0.85 as determined by ASTM D1894 with an 18.14 kg (4 lb.) pound sled. U.S. Pat. No. 6,087,015 is incorporated herein by reference in its entirety. U.S. Pat. No. 6,087,015 is incorporated herein by reference in its entirety.
U.S. Pat. No. 6,086,982 describes a biaxially oriented polypropylene film. The n-heptane-insoluble content of the film has a chain isotactic index, measured by  less than 13 greater than  C-NMR spectroscopy, of at least 97%. In addition, a process for the production of the polypropylene film and the use of the film are described. U.S. Pat. No. 6,086,982 is incorporated herein by reference in its entirety.
U.S. Pat. No. 6,074,762 describes a block-resistant film which comprises a core layer of a thermoplastic polymer having a first side and a second side; a functional layer which is printable or sealable or treatable for printing or sealing is on the first side of the core layer, and a block-resistant layer is on the second side of the core layer. The block-resistant layer comprises a thermoplastic polymer and an amount of a polydialkylsiloxane, based upon the entire weight of the block-resistant layer, sufficient to inhibit blocking of the block-resistant layer to the functional layer when they are in contact and which polydialkylsiloxane deposits silicon onto the functional layer but the amount of silicon deposited is not substantially detrimental to the printing function or the sealing function. U.S. Pat. No. 6,074,762 is incorporated herein by reference in its entirety.
In accordance with the present invention, there is provided a polymer film possessing a low coefficient of friction, which comprises:
(a) a core layer comprising a polyolefin wherein the core layer comprises the interior of the film;
(b) a first transition layer comprising a polyolefin and a silicone additive, wherein the first transition layer is exterior to the core layer; and
(c) a first skin layer comprising a polyolefin wherein the first skin layer is exterior to the first transition layer, and wherein the first skin layer is exterior to the core layer.
The advantages of the present invention include one or more of the following:
A film which can be sealed on both sides.
A film which can be treated on both sides.
A film which is composed of multiple layers.
A film which has high scratch resistance.
A film which has good slip properties
A film which is transparent
A film which has good printability
A film which has decreased coefficient of friction
A film which has decreased hot slip
A two-side treated, two-side sealable film using a silicon oil slip package
A film without loss of sealability after treatment
For a better understanding of the present invention, together with other and further objects, reference is made to the following description, taken together with the accompanying drawings, and its scope will be pointed out in the appended claims.